THE ZEROTH LAW OF THERMODYNAMICS

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27 Οκτ 2013 (πριν από 4 χρόνια και 11 μέρες)

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THE
ZEROTH

LAW OF
THERMODYNAMICS

If
two systems
are
in thermal
equilibrium with a third system
, they are
also in thermal equilibrium with each
other.

Example: Two thermometers measuring
the same body should give equivalent
values.

Notes: Laws of Thermodynamics

FIRST LAW OF THERMODYNAMICS

Whenever heat is added to a system, it transforms
to an equal amount of some other form of energy.

A system is any group of atoms, molecules, or
objects.

Example: steam engine: fuel is used to raise the
temperature of water to boil, the steam can turn a
wheel to make mechanical energy that can do work

Heat added

=

Increase in

internal energy

+

External work done
by the system

Another way of saying the first law:


The change in the internal energy of a substance is the sum of the
heat transferred plus the work done



Change in Internal Energy = Heat transferred + Work done


INTERNAL ENERGY

“internal energy”
is associated with the random
motion of
all of the molecules

that make up an object
-

the
more
molecules

there are, the
more internal energy

is possible.

Hot beverage

Massive iceberg

The iceberg has more internal energy because it has more molecules.

Heat Engines


A
heat engine
is any
device that changes
internal energy into
mechanical work


Power generation
plants use fuels to make
steam
-
driven turbines
that allow production of
electricity



Another
example is an
automobile
engine which
converts
gasoline into
motion.

Much of the energy released by

the combustion of fuel does not
produce the mechanical energy of
motion in the car.

In what form does much of that
released chemical potential energy
appear???


Heat
!

The First Law of Thermodynamics is yet
another way to state that energy is
neither created nor destroyed, but may
be transferred or
transformed
-


The Law of Conservation of Energy


2nd Law, The Law of Entropy:


Natural processes always increase entropy.

Entropy:
disorder

What does “entropy” have to do with
heat??

… Go back to the Kinetic
-
Molecular Theory:

The
faster atoms
are moving, the
more “disorder
” or
ENTROPY

they have.


So, if you increase the temperature of a substance,
you also increase its
ENTROPY
.


Just like water flows naturally from high elevation to low
elevation, heat flows naturally from
warmer temperature
to cooler temperature
.

Heat will never of itself flow from a cold object to a hot object.

You can make water move from low elevation to high
elevation if you use a
water pump
, which requires an
input of energy.

You can make heat flow from a cooler object to a warmer
object if you use a
heat pump
, which requires an input of
energy.

Heat pumps

are used in your refrigerator and in the
heating/air conditioning system in houses!


Different kinds of heat pumps:

Refrigerators remove heat from
food and transfer the heat to the
outside.

3rd Law: It is not possible to lower the

temperature to absolute zero.


Since absolute zero is the temperature at which
a gas would exert zero pressure
-

which is
impossible, reaching
0 Kelvins

is impossible
also.